docs: def list_pubs(self, buf):
          """SSH v2 public keys are serialized and returned."""
          assert not buf.read()
          keys = self.conn.parse_public_keys()
          code = util.pack('B', msg_code('SSH2_AGENT_IDENTITIES_ANSWER'))
          num = util.pack('L', len(keys))
          log.debug('available keys: %s', [k['name'] for k in keys])
          for i, k in enumerate(keys):
              log.debug('%2d) %s', i+1, k['fingerprint'])
          pubs = [util.frame(k['blob']) + util.frame(k['name']) for k in keys]
          return util.frame(code, num, *pubs)